[2gumby2]

I recently moved to a new apartment. After hooking up my stereo system, it seems that I have a ground loop as I have "hum" coming from my speakers. I did not have this problem at the house I moved from. I thought perhaps that it could be the wiring configuration at the new apartment. My integrated amp (Jolida JD1500RC) and CD player (Marantz DV9500) are plugged into different outlets on the same wall. To use a different outlet in the same room, I would need to run a 25 foot extension cord to the components. I'm not sure if the outlets have anything to do with this, but it's just a thought. Any suggestions on how to troubleshoot this? Both components have 3-prong extension cords. I have other components that I could swap out with 2-prong cords, but I prefer the Jolida/Marantz setup.

[Wayner]

Is your set up in the living room? Most outlets in this room have the top outlets controled by a switch to operate table lamps in that room. If you have table lamps, do any of them have a flousescent lamp in them?

[Jonathan]

Is your cable TV box connected to your system anywhere? (Are you running audio outs to your preamp from either the cable box or the TV to which the box is connected?)

 If so, get yourself a Calrad ground isolation transformer for about eight bucks. Worked like a charm on a wicked hum in my system. 

[richidoo]

The easy way to fix the hum is to isolate the grounds on the signals. As Jonathan suggested, the hum can come in on antenna, whether cable or FM (mine was from FM ground wire). You can determine where the loop is by selectively removing connections one at a time.  Remember though that ground hum is (usually) not a fault of a component, but simply different ground voltages between two components. The finest equipment in the world can have a ground hum. You can try to cure it with grounding techniques, but in my experience it is so much easier to put a transformer between them and be done with it. I was worried that would effect the signal quality, but it is not noticeable.

You can determine the limits of the wall circuit you are using by flipping circuit breakers. If the components are all on one circuit, likely not a ground loop caused by power ground. Even if two separate circuits, modern copper grounding is rarely at fault, unless you do something weird like put an antenna on the roof and ground it to the rod and coax.

Coax isolator - I have used this with good results
Calrad RCA isolator
Jensen - expensive, don't know if any better than Calrad

If not an antenna causing it, you can try to get all your components power plugs on the same circuit, even if different outlets. Worst case, and this is not recommended is to use a ground lift adapter to diagnose if it is a power plug issue or maybe ground connection broken inside a component. If the lift solves the problem, continue to use it with caution. If the fire marshall inpescts your burnt out house and finds this in use, you might not get any insurance money.

I bet it is your cable antenna and the reference ground on it is farther away that it was at your old house. Could be several miles. You might also wanna get a surge protector on that coax coming in, like this one. I have these and they don't affect signal at all.
Good luck gumby!
Rich

[boead]

ISO-MAX®
Model VRD-1FF

http://www.jensen-transformers.com/iso_vid.html

Cable TV RF Isolator
For Analog and Digital Cable TV and Cable Modems
Solves "Ground Loop" and "Hum Bar" Problems
(Supercedes the VR-1FF)


Cable TV will absolutely introduce a ground hum. I use one of these on the cable line coming into the system and its eliminated all the noise and the system is HiDef with On demand – all work great!

Also, I have two outlets close by the system and they can NOT be used together. Even with just one component (a sub across the room) powered by the ‘other’ outlet caused a hum. I had to run a long extension cord from the systems outlet to the sub – AND both outlets are on the same breaker. Go Figure? Both are properly grounded (I checked) and the electrical wiring in the house is excellent. I found (after some time) that this situation is fairly common.

I use two PS Audio Juice Bars from a single outlet. It accommodates my entire system. I use a furman power conditioner for TV and Surround components only while the 2-channel gear is left unfiltered but again, share the same outlet source.


http://www.psaudio.com/products/juicebar.asp


http://www.furmansound.com/product.php?div=02&id=ELITE-15

[Wayner]

I think you need to isolate the source of the hum rather than spend hundreds of dollars on equipment that may not solve the problem. Do you have cable or satelite in this system? Do the other components you use to swap with the Jolida and Marantz have 3-prong plugs?

[Bill Baker]

Interesting enough, just 10 minutes ago I finally traced a hum I have been trying to figure out for a week.
 It a Reference Jolida 801 and everytime I put it into my test system, I would get a hum. What the...........
 Finally, I decided to try a difference source so as I go behind the system to swap some cables to the different source, I realized I still had my S-Video cable hooked up to the DVD player I was using to test the amp. (I also have cable going into the TV. I normally leave the video cable unplugged but me and the family came down to watch a movie a few weeks ago). So, while the speakers are sitting there buzzing away, I unplugged the video cable......... Noise instantly disappeared. Now you can have your ear to the tweeter an not hear a peep.

 The funny thing is, I am usually the first person to tell someone with a noise problem to disconnect the video cable from the DVD player or disconnect any type of video signal.

[Wayner]

Response Audio,

A friend of mine was running his laptop into his system and discovered that his diplay from the laptop was causing a hum. The hum would vary by frequency (not 60 cycle) in accordance to the intensity of the display on his laptop. I can only explain this with poor internal shielding in the laptop. 

[boead]

If it’s the Cable Company’s signal causing the hum the IsoMax is under $60 and will work well. The other cheaper ones found at RadioShack will interfere with HiDef and On demand services, the Isomax won’t. It will also improve picture quality.

If cable isn’t involved then it can be two different outlets which is easy to check for and FREE to fix.

I had an issue once that was unsolvable and caused by a powered sub. I simply lifted the ground with a converter from Home Depot and it was solved but unfortunately that’s a band aid.

Power conditioners and isolated outlet strips won’t solve a ground problem. But they can improve the quality of your system IF its integrated with Video and/or computer gear which can introduce unwanted noise. A nice quality power outlet strip makes it easy to use a single wall outlet for a multitude of components. In direct side-by-side comparison, a PS audio Juice Bar sounds better then a Home Depot multi outlet splitter.

Computer power supplies can be horribly noisy and should be isolated or filtered from the rest of your Audiophile gear. Computer APS’s (battery backup devices) for computers and office equipment are also noisy, its entirely the wrong type of power supply for an audio system. Companies like Furman Sound make professional grade isolation, filtering, power regulation (battery) and balanced power transformers for both Pro Audio and Audiophile. There site has loads of information. Furman has been around for many years and is well know in the Pro-Audio Engineering and AV installation industries.

[2gumby2]

Thank you everyone for all of the great suggestions. I never thought about video as a source for interference. Here is some more information -

No flourescent bulbs in this room
No cable box, but I do have my cable TV hook-up going directly from the cable wall outlet into the TV. The DV9500 is connected to the TV via component video cables only (Used for DVD playback).
No antennas
No satellite
My other components that I could swap out do have 2-prong plugs

I tried using ground-lifter plugs on the units to see if it made a difference. It didn't. Hum still there.
When I go home later today, I'll try disconnecting the cable from the TV to see if there is a difference.

[Bill Baker]

No cable box, but I do have my cable TV hook-up going directly from the cable wall outlet into the TV. The DV9500 is connected to the TV via component video cables only (Used for DVD playback).
When I go home later today, I'll try disconnecting the cable from the TV to see if there is a difference.

 I still believe your noise will disappear when you disconnect the video cables from the DVD player. Even though you do not have any direct connections to your system, the cable "noise" is working it's way back to the system through the video cables. The best way to check would be to disconnect the video cables from the DVD player altogether and not just the cable from the TV.
 Better yet, disconnect all sources from the amp with only the speakers connected. This way you can eliminate the amp as the culprit.

[boead]

I tried using ground-lifter plugs on the units to see if it made a difference. It didn't. Hum still there.

Its the Cable TV!

Years ago I had ground hum when my computer was connected to the system via a digital cable to a DAC. For the sake of me I couldn’t figure what the problem was till I realized that I had CableTV going directly into my computer which had a TV Tuner built-in to the video card (ATI Radeon AIW). Removing the cable solved the hum problem but I wanted the TV on the PC. I used a “glass optical” TOSLINK from the PC to the DAC and the problem was solved.

You can call the cable company and complain but there will be little they can do.

The ISOMax works wonders.

[2gumby2]

Well, I disconnected ALL video connections and I still had hum. Then, disconnected the audio input from the DV9500 and still had hum. I even ran an extension cord from various outlets in the room and still had hum. So I removed the Jolida and replaced it with my Onkyo receiver (uses a 2-prong plug) that I had in the bedroom system and the hum was gone. I put the Jolida in the bedroom system and did not have a hum problem. I have no idea why the living room interacted with the Jolida to produce hum. A mystery that I will not likely solve.

Thanks everyone for all of your input!

[DSK]

Given your test results, it sounds as though lifting the ground on the Jolida would kill the hum. But, we know that is an unsafe practice. So perhaps this device would be your best option ... it should perform the same feat while keeping your ground in tact and avoiding putting anything in the signal path.

http://www.ebtechaudio.com/humxdes.html

[Bill Baker]

Hmmmm........ strange. I can't tell from what you wrote but did you disconnect everything from the amp except the speakers? This will tell you for sure if it's coming from your AC line. It is obviously not the amp as it does not create any hum in your other system.
 From your system picture, it looks like you may have the amp plugged into a Monster Conditioner? If so, unplug it from this and plug it directly into the wall. Tube amps don't always like being plugged into conditioners or power strips.

 Don't give up on this one. In the end, it will probably turn out to be the most simplest thing.

[2gumby2]

I have disconnected all sources leaving only the speaker wires connected and still have hum. As I continued to investigate, I realized that there is actually some hum in the second system as well. I didn't notice it initially I suppose because of the difference in sensitivity of the two speaker systems (97db vs. 86db). I only noticed hum in the less efficient speakers when I put my ear right next to the tweeter. I wonder if what I'm hearing is some kind of "tube rush" from the preamp section.

[Bill Baker]

This is getting stange now. How old is the unit and/or tubes? It could be a tube related issue. Dealing with 97dB speakers will definitely bring out any noise associated within a system.
 As I mentioned, I have two of these in my home and have run one of them with a pair of 98dB Usher D2 Horns. Even in this system, you could only hear a slight noise when placing your ear just at the horn (10 inches from the TAD driver).

 12AX7/5751 tubes can be had on the cheap, if you can, it may not hurt to try another set of tubes. Another consideration, how is the electrical wiring? Do you have any appliences on the line? Last question, is the hum effected by the volume control or consistent no matter what the volume setting??

[richidoo]

Ken Bernacky from Stereo Surgeons  wrote to me a few months ago about ground hum and it was very helpful to me to understand what is really going on and dispel my misunderstandings. Maybe this will be of slight help to you. Listening to my tuner's RCA output with headphones (using ratshack adapter) proved to me that there was nothing wrong with the tuner and let me move my mind onto solutions instead of making up problems as I am prone to do... Here is his email:

"Assuming you actually do have a ground loop:  A ground loop exists in any installation because there is a difference in potential between the two, or more, "grounding points".  Being at ground potential is not an absolute, there is no such thing as 0 volts, there is more and more precision, ie: 0.1 v, 0.01 v, 0.001 v, etc., all can be considered to be at ground potential for certain applications.  The problem develops when we connect an audio amplifier chain with it's large associated gain, typically 100 dB. or greater.  What in one situation without such gain would be an adequate ground the large gain situation magnifies this seemingly small difference in potential, say 0.01 v to an audible level of 60 hz. hum.  What is clear is this pipe in the dirt ground is not at the same ground potential as the amplifier chain ground and thus your 60 hz. hum.  You never said it is 60 hz. hum, I'm assuming this.  I am also assuming that even with the tuner turned off you get the hum, as you specifically said it is not affected by the (tuner?) volume control.  I also suspect if you had headphones connected to the tuner output and had no interconnecting cables to the amplifier chain the currently perceived hum would not exist.  I suspect the difference in ground potential current is flowing down the coax, going over the interconnecting cable's shield from the tuner to the input of the amplifier, thru the amplifier to whatever the amplifier is using as it's "ground" point in your home.  This current flow is being coupled, possibly capacitively in cables, amplified, and you hear it as hum.

"To do this properly this difference in ground potential between all ground points must be reduced further, you will never get it to absolute 0, but below the level at which an audible hum occurs.  This can be done by running the ground point for the amplifier chain to the ground you are using for the antenna with the largest sized wire possible.  The larger wire has lower resistance and this whole problem is occurring because of a voltage being developed because of current flow thru the resistance of the wire.  Since ohm's law states E=IR, stated another way: Voltage = (Current)(Resistance) one can see that reducing the resistance of the wire lowers the offending voltage, BUT IN THIS CASE THE VOLTAGE MUST BE REDUCED TO AN EXTREMELY LOW VALUE DUE TO THE LARGE GAIN OF THE AMPLIFIER CHAIN.  This may turn into a ridiculous extreme and is not what I would do.  First of all I don't know why you "grounded" the coax.  I would not do that.  Assuming you wanted lightning protection I would get the type of lightning arrestor which uses a small gap between the coax and the line run to "ground".  This would provide lightning protection and not cause a ground loop.  Also your tuner uses a 3.3 mohm resistor from one side of the AC line to the chassis, reversing the ac plug in the wall may affect the hum situation.

"Ground loops can be frustrating because the neophyte thinks ground is ground, but once one experiences the epiphany that nothing is at the same ground potential when connected thru wiring (thru resistance), and this difference in ground potential causes a current flow, then it all begins to make sense.  Usually in cases like this the fewer ground points the less problems one has.  As an aside...on circuit boards many times foil patterns are designed to specifically not have currents flow thru certain "ground" areas because this seemingly infinitesimally small current gets amplified and adversely affects circuit operation.  To prevent this the circuit board designer uses a technique called star grounding, actually what you are currently doing is a crude form of star grounding, just not good enough due to the extreme gain of the amplifier chain.

"Sincerely,

Ken Bernacky
President, Stereo Surgeons, Inc.
http://www.stereosurgeons.com"

[2gumby2]

The unit is 5 moths old with the original tubes. The apartment is very well maintained so I expect the wiring to be in good condition. No appliances in the chain. I don't know anything about the quality of the stock tubes so I think I'll order some 12AX7 tubes from Van Alstine and see what happens. It could just be some tube rush.

[2gumby2]

I forgot to mention that hum is independent of volume level.